Propylene-based elastomers, which may also be referred to as semi-amorphous propylene copolymers or crystallizable propylene-based copolymers, have been employed in the manufacture of fibers and non-woven fabrics. These copolymers are often blended with other polymers in the pursuit of sundry desirable properties.
For example, U.S. Pat. No. 6,342,565 teaches blends of crystallizable propylene-based polymers with predominately crystalline propylene-based polymers. The crystallizable propylene-based polymers are characterized by a melt temperature of less than 105° C. and a heat of fusion of less that 45 J/g. The predominately crystalline propylene-based polymers are characterized by a melt temperature greater than 110° C., a heat of fusion greater than 60 J/g, and a molecular weight of 10,000 to 5,000,000, with a polydispersity between 1.5 and 40. Fibers made from these blends purportedly have decreased flexural modulus and an increased load capacity, as well as low values of set and load decay.
U.S. Publication No. 2005/0107529 teaches fibers prepared from propylene-based elastomers. For example, Example 1 teaches the production of fibers from a melt that contains a 20 MFR propylene-ethylene copolymer containing 15 weight percent ethylene together with a propylene homopolymer. The propylene homopolymer is either a 36 MFR homopolymer or a 400 MFR homopolymer. The fibers are formed by employing a conventional fiber spinning line in partially oriented yarn mode. Similar blends are spun bonded within Example 2. The fibers and non-wovens prepared therefrom can be heat set to provide durable fabrics.
U.S. Publication No. 2005/0106978 teaches fibers and non-wovens prepared from blends that include a crystalline isotactic polypropylene polymer and an α-olefin copolymer, which is a propylene homopolymer or random propylene copolymer in which the propylene stereoregularity is disrupted by comonomer. The copolymer is characterized by a heat of fusion, as determined by DSC, of from 1.0 J/g to 50 J/g. The blend may include additional components such as additives, process aids, tackifying resins, plasticizers, slip aids, fillers, curatives, and the like. The resulting fabrics are elastic and are useful in personal hygiene products such as diapers, in medical fabrics, and in consumer products.
U.S. Publication No. 2006/0172647 teaches fibers and non-wovens prepared from polymeric blends that include a semi-crystalline polymer and a semi-amorphous polymer. The semi-crystalline polymer is characterized by a melting point between 100° C. and 160° C., a melt flow rate from 0.2 to 2,000 dg/min., a 1% Secant Flexural Modulus of from 1,031 to 1,720 MPa, and a heat of fusion greater than 60 J/g. The semi-amorphous polymer includes propylene and 10 to 25% by weight units deriving from α-olefin monomer. The semi-amorphous polymer is characterized by a crystallinity of from about 2.5 to about 35% by weight, a melting point of 105° C. or less, and a heat of fusion of less than 70 J/g. Non-woven articles produced from these blends have a Hand of 40 g or less at a fabric basis weight of 35 gsm.